(19)
(11) EP 0 932 091 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
11.08.1999 Bulletin 1999/32

(43) Date of publication A2:
28.07.1999 Bulletin 1999/30

(21) Application number: 99400128.7

(22) Date of filing: 20.01.1999
(51) International Patent Classification (IPC)6G05B 23/02
(84) Designated Contracting States:
AT BE CH CY DE DK ES FI FR GB GR IE IT LI LU MC NL PT SE
Designated Extension States:
AL LT LV MK RO SI

(30) Priority: 20.01.1998 US 8869

(71) Applicant: COMPRESSOR CONTROLS CORPORATION
Des Moines Iowa 50322 (US)

(72) Inventors:
  • Mirsky, Saul
    West Des Moines, Iowa (US)
  • Staroselky, Naum
    West Des Moines, Iowa (US)

(74) Representative: Picard, Jean-Claude Georges 
Cabinet Plasseraud 84, rue d'Amsterdam
75440 Paris Cedex 09
75440 Paris Cedex 09 (FR)

   


(54) Method and apparatus for limiting a critical variable of a group of compressors or an individual compressor


(57) This invention discloses a method for limiting a critical variable (such as, discharge pressure or suction pressure or pressure ratio) of either a compressor station or an individual compressor when these machines are subjected to large, fast disturbances. Each configuration, whether a station or an individual compressor, is equipped with two PID controllers: (1) a main controller for compressor critical variables and (2) a limiting controller that participates in modulatiag recycle valves. At the onset of sudden, large changes of mass flow at a compressor's or station's discharge, the effectiveness of the two controllers (acting independently) may be insufficient to prevent discharge pressure from reaching the shutdown set point which, in turn, disrupts the process supported by the compressors, and the longevity of the drivers is diminished. For these reasons, this disclosure relates specifically to a technique that combines the functions of the main and limiting controllers. Because of the complementary (synergistic) interaction of the controllers, an earlier and faster opening of the antisurge valves is initiated, and pressure at the discharge header is effectively limited.





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